The correct increasing order of the second ionization enthalpies of C , N , O and F is :

Step-by-step solution

Second ionization enthalpy ( IE ₂ ) is the energy required to remove an electron from the univalent gaseous cation ( M^+ ). The valence electronic configurations of the univalent cations are: C ^+ : 2s^2 2p^1 N ^+ : 2s^2 2p^2 O ^+ : 2s^2 2p^3 F ^+ : 2s^2 2p^4 The O ^+ ion has an exactly half-filled 2p^3 subshell, which imparts extra stability. Removing an electron from this stable configuration requires exceptionally high energy, making the IE ₂ of oxygen the highest among these four elements. For the remaining ion